The present invention relates to a valve means for use with an anesthesia breathing circuit, and more particularly, to a positive-end expiratory pressure (PEEP) valve which is adapted to maintain a predetermined minimum pressure at all times within the lungs of a patient during ventilation.
It is presently known that, in some patients, a positive-end expiratory pressure is needed during ventilation in administering anesthesia or, for that matter, in maintaining a patient on a respirator. With PEEP, the patient is allowed to exhale only to a point where a positive pressure is maintained within the lungs so that at all times the lungs are maintained at or above their normal resting volume. The maintenance of such a positive pressure may prevent alveolar collapse.
Various devices are currently available which do accomplish PEEP during respiration, however, the present devices also introduce a not insignificant fixed resistance into the breathing circuit so that the patient exhales against the resistance of the PEEP device as well as the other internal resistance and pressure on the downstream side of the circuit itself. Any additional resistance in the circuit due to the PEEP device is, of course, undesirable since it tends to reduce the rate at which exhalation occurs.
In the present invention a PEEP valve is provided for placement in a patient breathing circuit between the ventilator bellows or bag and the remaining parts of the circuit. At this point in the circuit, the gas flow during respiration is bidirectional. The valve has two parallel gas flow paths; one of which includes a check valve to preclude gas from returning to the bellows or bag via that path, and the second flow path provides a diaphragm valve which opens and closes in accordance with the pressure in that flow path. The diaphragm valve is adjustable to operate at a pressure within a range of desired minimum pressures since each patient may require a different residual pressure in the lungs. By the construction of the valve, and its particular position in the circuit, minimal resistance is introduced into the patient circuit itself.
Thus, a valve is provided which allows an adjustable, accurate establishment of a PEEP in a patient circuit without also introducing a further fixed resistance which could reduce the exhalation rate of the patient.
A basic patient breathing circuit on which the present invention is an improvement, is shown by U.S. Pat. No. 3,556,097, granted Jan. 19, 1971 to D. R. Wallace for "Disposable Anesthesia-Breathing Circuit Unit" and assigned to the same assignee as the present invention.